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The Mole

The Mole. Chapter 11: The Mole ____ 11.1 Measuring Matter ____ 11.2 Mass and the Mole ____ 11.3 Moles of Compounds ____ 11.4 Empirical Formulas and Molecular Mass ____ 11.5 The Formula for a Hydrate . 11.1 Measuring Matter Counting Particles

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The Mole

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  1. The Mole

  2. Chapter 11: The Mole • ____ 11.1 Measuring Matter • ____ 11.2 Mass and the Mole • ____ 11.3 Moles of Compounds • ____ 11.4 Empirical Formulas and Molecular Mass • ____ 11.5 The Formula for a Hydrate

  3. 11.1 Measuring Matter • Counting Particles • What is a mole (commonly abbreviated mol) • The mole is the SI unit to measure the amount of a substance. • It is the number of representative particles, carbon atoms, in exactly 12g of pure carbon-12.

  4. A mole of anything contains 6.02 X 1023 representative particles. • A representative particle is any kind of particle such as atoms, molecules, formula units, electrons, or ions.

  5. Avagadro’s Number (6.02 X 1023) 602,000,000,000,000,000,000,000,000 • Converting Moles to Particles and Particles to Moles

  6. 1. 2.5 mol Zn X • = 1.51 X 1024 atoms Zn • 2. 3.25 mol AgNO3 X • = 1.96 X 1024 formula units AgNO3 • 3. 11.5 mol H2O X = 6.92 X 1024

  7. Converting Particles to moles: simply multiply the number of particles by the conversion factor.

  8. Ex: Calculate the number of moles that contain 4.5 X 1024 atoms of Zn.

  9. 4. a. 9.55 mol Al • b. 6.23 mol CO3 • c. 0.595 mol ZnCl2 • d. 4.15 X 10-4

  10. Section 11.2 Mass and the Mole Molar mass The mass in grams of a mole of any pure substance is called its molar mass. The molar mass of any element is equal to its atomic mass and has the units g/mol. Ex. An atom of manganese has the atomic mass of 54.94 amu. Therefore its molar mass is 54.94g/mol

  11. Mole to Mass Conversion Ex. What is the mass of 3.00 moles of Mn. • Conversion factor is 1 mole Mn = 54.9g

  12. Answers • 11. a. 96.3 g Al • b. 1.2 X 103 g Si • c. 203 g Co • d. 1.6 X 102 g Zn

  13. Mass to Mole Conversion Ex. How many moles are there in 525g calcium?

  14. Answers • 12. a. 0.236 mol Ag • b. 9.355 mol S • c. 1.91 mol Zn • d. 17.9 mol Fe

  15. Conversions from mass to atoms and atoms to mass (this a two-step process) • Ex. How many atoms are in a 25g sample of pure gold?

  16. Ex. How many atoms are in a 25g sample of pure gold? • Step 1 • Multiply the mass of gold by the molar mass conversion factor:

  17. Ex. How many atoms are in a 25g sample of pure gold? • Step 2

  18. Answers • a. 4.79 X 1024 atoms Li • b. 6.68 X 1020 atoms Pb • c. 3.45 X 1022 atoms Hg • d. 9.77 X 1023atoms Si • e. 1.51 X 1024 atoms Ti

  19. Note: Mass must always be converted to moles before being converted to atoms, and atoms must first be converted to moles.

  20. Although this is a two step process , you can make this conversion in one step. • Ex. How many molecules are in 1.00 g of H2O?

  21. Ex. How many molecules are in 1.00 g of H2O? • You can set up the calculation like this: • The units all cancel to give the answer in molecules of H2O.

  22. Answers • a. 2.09 X 103 g Bi • b. 91.3 g Mn • c. 0.226 g He • d. 3.49 X 10-8g N • e. 5.93 X 10-7 g U

  23. The Molar Mass of Compounds A mole of a compound would contain Avagadro’s number of molecules of that compound. • The mass of a mole of a compound equals the sum of the masses of every particle that makes up the compound.

  24. The Molar Mass of Compounds • Ex. What is the mass of potassium chromate (K2CrO4)? • Use the periodic table to find the molar mass of each element and multiply it by the subscript. • K 39.1g X 2 = 78.2g • Cr 52.0g X 1 = 52.0g • O 16.0g X 4 = 64.0g • Molar mass of K2CrO4 = 194.2g

  25. NaOH – 40.00 g • CaCl2 – 110.98g • KC2H3O2 – 98.14 g • Sr(NO3)2 – 211.64g • (NH4)3PO4- 149.10g

  26. C2H5OH – 46.07g • C12H22O11- 342.30 g • HCN – 27.03 g • CCl4- 153.81 g • H2O – 18.02g

  27. Converting Moles of a gas to volume • One mole of any gas at Standard Temperature and Pressure, occupies a volume of 22.4 Liters • STP – Standard Temperature and Pressure (room temp-25oC) (pressure at sea level 101kPa)

  28. Converting Moles of a gas to volume • Ex. What is the volume of 2.5 moles of gas at STP? • 2.5 mol X = 61L of Gas • Ex What is the volume of 2g of H2 gas at STP? • First convert mass to moles. • 2gH2X 1 mole H2 X = 22.4L H2 2 g H2

  29. Empirical and Molecular Formulas • Percent Composition from the chemical formula • The percent by mass of all the elements of a compound is called the percent composition of a compound.

  30. Percent Composition from the Chemical Formula • Calculate the mass of each element in a compound and divide this value by the molar mass of the compound • Ex. What is the percent composition of H and O in water H2O • Mass of H = 2 X 1.01g • Mass of O = 16.00g

  31. Ex. What is the percent composition of H and O in water H2O

  32. Empirical Formula • The empirical formula for a compound is the smallest whole number ratio of the elements.

  33. Molecular Formula • Molecular Formula specifies the actual number of atoms of each element in one molecule or formula unit of a substance.

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